1. Technical Field of the Invention
The present invention relates generally to an alternator which may be installed in passenger automobiles or autotrucks, and more particularly to such an alternator designed to have enhanced cooling ability to cool a stator winding.
2. Background Art
International Patent Publication No. WO9206527A1 discloses an automotive alternator which is equipped with a stator having a winding formed by a plurality of U-shaped conductor segments joined together. The formation of the winding is achieved by inserting the conductor segments into slots of a stator core from one of opposed ends of the stator core and joining ends of the conductor segments extending from the other end of the stator core. This type of winding has the advantage that the space factor of the conductor segments in the slots of the stator core is improved as compared with a winding formed by turns of a single conductor, which results in a decreased electrical resistance of the winding, thus decreasing the heat generated in the winding. Use of the conductor segments enables turns of the winding to be arranged regularly, thereby minimizing physical interference between portions (which will also be referred to below as coil ends) of the conductor segments extending outside the ends of the stator core and enhancing the efficiency of flows of cooling air through the coil ends. This permits the length of the coil ends to be decreased, thereby further reducing the electrical resistance of the winding or the amount of heat generated in the winding.
Japanese Patent No. 3456140, assigned to the same assignee as that of this application, discloses an alternator equipped with a stator winding which is wound in a stator core to have a stator blade-shape at the coil ends, thereby improving the cooling ability of the alternator to cool the stator winding.
The use of the conductor segments in making the stator winding as taught in the former publication enables high-power small-sized automotive alternators to be made. Such a type of alternator is, however, still required to enhance the cooling ability to cool the stator winding in order to increase the output power further. This may be achieved by forming radiator fins on the coil ends of the conductor segments to cool the coil ends effectively.
In the case where the radiator fins are formed by extending the ends of the conductor segments connected by joining only tips of the ends, as disclosed in the latter publication, to be long outside one of the axially opposed ends of the stator core, the cooling ability is enhanced, but however, the increased length of the conductor segments leads to increases in electrical resistance thereof and amount of heat generated. This results in the disadvantages that the temperature of the stator winding is not reduced sufficiently and an increased copper loss causes torque required by the alternator to rise, thus leading to a decrease in efficiency of generation of electricity in the alternator.
Japanese Patent First Publication No. 2001-238386 that is an equivalent of U.S. Pat. No. 6,448,681 discloses an alternator equipped with a stator winding made of conductor segments connected by electrically welding tips of ends of the conductor segments extending outside an end of a stator core. This type of alternator, however, like the structure taught in the above Japanese Patent No. 3456140, has the problem of increase in electrical resistance of the stator winding.